Some Physics Questions?

Question

I'm just wondering how you would come to the right answers for some questions:

1) A 1000 kg truck has an inital velocity of 10 m/s. It accelerates until it has a velocity of 20 m/s. How much work was done by the engine? Answer: 150 000 J

2) I throw a 100 g object into the air. It reaches a maximum height of 2.0 m above my hand, which is 1.1 m above the ground. What's the total energy (potential and kinetic) at the top of the path

a) relative to my hand? Answer: TE = 2.0

b) relative to the ground? Answer: TE = 3.0

Answer 1

1) A 1000 kg truck has an inital velocity of 10 m/s. It accelerates until it has a velocity of 20 m/s. How much work was done by the engine? Answer: 150 000 J

Work = Kinetic energy in this case

KE = ½mV²

KE = ½(1000)(10)² = 50000 Joules

2) I throw a 100 g object into the air. It reaches a maximum height of 2.0 m above my hand, which is 1.1 m above the ground. What's the total energy (potential and kinetic) at the top of the path

a) relative to my hand? Answer: TE = 2.0

100g = 0.1 kg.

weight = 0.1*9.8 = 0.98 N

Potential energy = wh = 0.98*2 = 1.96 J, close

b) relative to the ground? Answer: TE = 3.0

Potential energy = wh = 0.98*3.1 = 3.04 J, close